A redundant array of independent disks (RAID) apparatus includes two or more power supply units (PSUs) each of which supplies electric power to each controller module (CM).
When a parallel redundant operation of the PSUs is performed, an output from the two or more PSUs is supplied to the CM through a back plane (BP) as a single output. In addition, when a malfunction occurs in an output of a PSU, the PSU self-detects the output malfunction and stops the output or performs malfunction notification. However, on the occasion that an internal control circuit or an internal power source circuit in a PSU breaks down, the PSU may not detect the malfunction and not stop the output.
When an overvoltage malfunction occurs in which the output voltage of a PSU increases more than a target voltage, a CM may be able to detect the overvoltage malfunction because a voltage supplied to the CM through a BP increases. However, on the occasion that a PSU may not self-detect a malfunction, it is difficult for a CM to identify a PSU in which an overvoltage malfunction occurs, from among two or more PSUs because malfunction notification is not performed from the PSU.
In addition, in a case of a low voltage malfunction in which the output voltage of a PSU falls below a target voltage, a CM may not detect a low voltage malfunction as long as one of two or more PSUs normally functions because a voltage supplied to the CM through a BP does not vary. In addition, when a PSU may not self-detect a malfunction, the PSU does not output a malfunction notification, so that a CM may not detect a low voltage malfunction.